1. Field of the Invention
This invention relates to a method for coupling external antennas to a communications unit. The invention also relates to an arrangement for coupling external antennas to a communication unit. The invention also relates to an antenna arrangement for coupling external antennas to a communication unit, which is arranged for establishing a first and a second mobile communication connection. The invention also relates to a communication unit, which is arranged for establishing a first and a second mobile communication connection.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
There are various mobile communication means known today, such as mobile stations, which enable having a mobile communication connection to a data transfer network, for example a Public Land Mobile Network (PLMN) according to the GSM specifications, generally via a base station serving a cell of the network. Antennas installed as fixed in these devices are used for sending and receiving radio frequency signals. The frequency range of mobile stations, e.g. the frequency range available in some GSM networks comprises the range 880-960 MHz. The frequency range available for modern mobile communication means, such as mobile stations, which use multiple frequency ranges, can also comprise the range 1710-1880 MHz (so-called DCS or PCN) or the range 1850-1990 MHz (so-called DCS or PCS). Two-way, independent data transfer is usually possible in each frequency range.
Various electronic devices, such as portable personal computers (PC) are often provided with an extension card connection, to the slot of which an extension card according to the standard can be connected. A known extension card is the PC card according to the PCMCIA (Personal Computer Memory Card International Association) standard. These extension cards form a functional entity with a PC. The extension cards can also contain radio parts with antennas, whereby the cards constitute a communication unit for mobile communication, a mobile station. Thus a PC can be connected to a data transfer network, such as a GSM network, by means of this card unit. The unit can also be intended for forming a Wireless Local Area Network (WLAN), whereby the unit is directly connected to other devices or a local area network via an Access Point, for example. In a local area network of devices and communication units, which is arranged for a data transfer connection of Low Power Radio Frequency (LPRF) or Short Range Radio Frequency (SDRF), the frequency range available comprises the range 2.4-2.5 GHz, i.e. 2400-2500 MHz.
The communication units mentioned above often also include coupling means for connecting an external antenna to the unit. This is often realized by using connectors, such as a coaxial connector or a BNC connector (Baby N Connector), and a flexible coaxial cable. An external antenna can be located on the outside of a vehicle, for instance, while the unit is used inside the vehicle. Thus the antenna is located in a free space, whereby the body of the vehicle causes less disturbance to the radiation pattern of the antenna. The body of a vehicle disturbs the operation of the fixed antenna of a unit located inside the body, whereby the operation radius of the antenna is often decreased considerably. The mobile station also has a fixed, protruding antenna, but the antenna switch in the device automatically detects the coupling of an external antenna and switches the fixed antenna off. It is also advantageous to locate the antenna of the card unit further from electronic devices causing electromagnetic interference, such as PC devices. An external antenna can then be coupled to the units via a cable. The antenna can be, for example, a monopole antenna, a helix antenna, a microstrip antenna or a so-called PIFA antenna (Planar Inverted F Antenna).
It is also common that an antenna intended for a local area network, which also has a smaller radius of operation, is integrated into the communication unit. Small-sized strip antennas and PIFA antennas are especially suitable for integration, generally as disposed on the circuit board of the card. Units that can be used both in a mobile communication network and a wireless local area network are also being developed. In such a construction, separate radio parts are placed in the unit, including transceivers for different networks and separate fixed antennas for processing signals of different strength and different frequency ranges.
The radiating antenna creates an electromagnetic field around it, by means of which it is coupled to other antennas, particularly intensely at a close distance from the antenna. When the size of communication units decreases, the problem becomes more pronounced, because it is not possible to increase the distance between the antennas. Often the way of using the communication unit or its design considerations, especially if it is a card unit, force the antennas to be located in a certain place and close to each other. The coupling causes spurious frequencies to be formed and carried to a transceiver coupled to an antenna, thus interfering with data transfer and its reliability. Spurious frequencies also radiate outwards, interfering with other devices as well.